Vibration reduction in mechanical systems is important for a number of reasons, including safety and energy efficiency of the systems. Particularly, vibration in various transportation systems is directly related to ride quality and safety of passengers, and, thus, should be minimized. For example, vertical vibration in vehicles can be controlled by active or passive vibration reduction systems, which are generally referred as suspension systems. Similarly, the vibration induced during an operation of an elevator system can be minimized.
The elevator system typically includes a car, a frame, a roller guide assembly, and guide rails. The roller guides act as a suspension system to minimize the vibration of the elevator car. The car and roller guides are mounted on the frame. The car and frame move along the guide rail as constrained by the guide rollers. There are two principal disturbances which contribute to the levels of vibration in the car: (1) rail-induced forces which are transmitted to the car through the rail guides due to rail irregularities, and (2) direct-car forces such as produced by wind buffeting the building, passenger load distribution or motion.
Some methods, e.g., a method described in U.S. Pat. No. 5,544,721, U.S. Pat. No. 5,329,077, compensate for irregularity of the guide rail in the elevator system to improve the ride comfort. However, the method measures the irregularity of the guide rail with sensors, which is expensive. Also, for the complex elevators systems, controlling the elevator car based only on the horizontal irregularities of the rails can be ineffective.
Specifically, controlling vibration of the elevator car of the elevator system is complicated by the difficulties in determining a state of the elevator system during its operation. Therefore, various systems for controlling lateral vibration of the elevator cars use simple control logic to determine the damping force compensating the disturbance according to detected vibration level. For example, a system described in U.S. Pat. No. 7,909,141 schedules the damping coefficient of a damper according to the travel speed of the elevator car. The resultant control system is not optimal, because the travel speed of the elevator only partially reflects the characteristics of the disturbance. Other methods require various sensors to implement a sophisticated control. For example, a control system described in U.S. Pat. No. 8,011,478 requires position sensors and accelerometers. Such method is expensive.